A High Capacity Bilayer Cathode for Aqueous Zn-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Aqueous zinc-ion batteries (ZIBs) are attractive for grid-scale energy storage due to safety and cost advantages.
• The performance of ZIBs is significantly limited by the cathode materials currently available.
• Developing high-performance cathode materials is crucial for advancing ZIB technology.

Purpose of the Study:

• To investigate Ca0.67V8O20·3.5H2O (CaVO) nanobelts as a novel cathode material for aqueous ZIBs.
• To elucidate the structure-property relationships governing the electrochemical performance of CaVO.
• To understand the ion-exchange and intercalation mechanisms within the CaVO cathode.

Main Methods:

• Synthesis of CaVO nanobelts.
• Electrochemical characterization including discharge capacity, energy density, and cycling stability tests.
• Combined theoretical (e.g., DFT) and experimental studies to analyze the crystal structure and ion transport.

Main Results:

• CaVO nanobelts achieved a high discharge capacity of 466 mAh g−1 at 0.1 A g−1 with excellent energy density (345.6 Wh kg−1).
• Remarkable capacity retention was observed: 100% after 500 cycles, 95% after 1000 cycles, and 74% after 2000 cycles at 5.0 A g−1.
• The bilayer ρ-type V2O5 structure facilitates efficient Zn2+ transport and reversible single-phase intercalation/deintercalation.
• Ca2+ acts as a structural stabilizer, undergoing ion exchange with Zn2+, and water molecules participate in the intercalation process.

Conclusions:

• CaVO nanobelts exhibit superior electrochemical performance, making them a promising cathode material for high-energy aqueous ZIBs.
• The unique structural features of CaVO, including the V2O5 framework and Ca2+ stabilization, are key to its high capacity and durability.
• Controlling precursor solution pH and the presence of Ca2+/Zn2+ and structural water are critical for CaVO synthesis and stability.